Electric measuring instrument.



H. 0. SPEGHT. ELECTRIG MEASURING INSTRUMENT. APPLICATION FILED DEC. 2, 1909.

megs.

INVENTOR ATiORNEY Pafiefited Dec, 10, 1912.

" E STA EsQPATENTfoFFIoE. Y

HANS C, SIECiHT; F BITTSBURGH, PENNSYLVANIA, ASSIGNOR, TO WESTINGHQUSE ELECTRIC AND MANUFACTURING COMPNY, A CORPORATION OF PENNSYLVANIA.

ELECTRIC MEASURING INSTRUMENT.

Specificationof Letters Patent.

. PatentedDec.10, 1912.

Application'filed December 2, 1909. Serial No; 531,056.

To all whom 'it may concern:

3 Be it-known that I, HANS C. Srncrrr, a

object to provide, in a system of the class above indicatedfmeans for accurately determining slight variations from a predetermined relatively large current.

, It often desirable to measure relatively slight variations from apredetermined cur rent value and this has heretofore been ditficult to accomplish accurately since, al-

thoughthe variations. could easily be read on the lower scale of a twoescale Instrument, it was impossibleto employ this scale for the l aggregate ciirre'nt flowing in" the circuit.

For example, in determining the core loss of a dynamo-electric machine, which is. driven by an electric motor, the current supplied to the driving motor under one field excitation of the machine being tested might be approximately 100 amperes, which would 'be read on a 150 ampere scale, while, under another field excitation, the current supplied to the driving motor might be 103 and a fraction amperes, which must also be read on the 15O 4a1npere scale. While the error of each of the current values read might be relatively small, if the errors were in the same direction, the error which would result when thedilference' of the two quantities was obtained would be relatively great since this difierence is a small quantity.

An ammeter of a well known type, such as f is illustrated in Patent 392,387, granted to Edward Weston; November 6, 1888, when adapted for measuring values of electric currents, comprises a constant magnetic field; usually produced by a permanent horse-Shae magnet, a coil rotatably mounted in the field oi the magnet, a pointer or indicator attached to the coil,'a suitable resist ance in series with the coil and one or more shunts of relatively low resistance connected across the terminals of the meter.

According to my present invention, I interpose a variable resistance between an in termediate oint in a current-measuriu' instrument, w liich maybe the junction 0 the ous'ly interrupted.

movable coil and the meter resistance, and the side of the circuit which is opposite that a to which the meter resistance is connected in orderto regulate'the amount of current flowing in the movable coil. -The regulating energy may, of course,'be produced by any suitable source and the resistance may be regulated until the pointer of the measuring instrument, which is connected for reading on the lower scale, is brought to zero. Under these conditions, the meter proper, exclusive of the shunts,is cut oil? from its source of current supply and the circuit con- .necting the intermediatepoint in the'meter with the variable resistance is simultane- If lieicond1t1ons are so changed that the current fiowingthrough the circuit is increased by a relatively small increment, the meter may lie again connected in circuit, the variable resistance circuit being closed at the sameQtime. Thereupon the pointer of theinst -rument wiil indicate, not the aggregate curreiit flowing in the circuit, but only the difiei'ence between the current flowing at the time when 'the adjustment to zero was eflected, and at the time of the reading.

"invention is illustrated in the accomp'anying drawings in which Figure 1 is a diagrammatic view of a system of electric current' measurement arranged in accordance therewith, and Fig.2 is a partially diagrammatic view of a measuring instrument, which may be advantageously employed in a system of the class illustrated in Fig. 1.

} Referring to the drawings, electrical energy may be supplied from any suitable I source, such as generator 1 to an electric motor-'2; In one side of the motor-supply circuit, low resistance shunts 3 and- 4: are included in parallel and an ammeter 5 is connected a'cross the shunt 3. -The ammeter 5' comprises a permanent stationary horse-shoe magnet 6, a rotatably mounted coil7, a twoscale dial v8, a pointer 9., and a resistance'lo, which is connected in series with the 'mov-' able coil 7. Variable resistances. 11 and 17 are connected from a point between the movable coil 7 and'the resistance 10 to the opposite side'of the supply line. The resistance 17 is preferably-calibrated so that it may be adjusted to compensate approi imately for the current traversing. the meter coil 7 when it is connected or=low-scale inswitch 12 is adapted to .simultaneousl break and make-the shunt circuit in wh ic the shunt 3. A single polesingle-throw 'swi'tclr 13 is adapted to exclude the shunt 4 I the instrument. I

- the system correspond in; F

- switches 12 and'13 areTs'u'ccessivelyiiop d;

.; taining accurately the cor. electric machine. but ji any specificianplicatieii, 1

and the switch 12 closedgthe only indicate 7 some small ifv'alue close to \the zero point. The reslsta ce1,1-

zero. If the load-foilgthe' mot rect reading of the ldifi'erence be ment unless itQis counteract ed bv the noriiial low resistance shur'z'connccti'on to'the'in dications' and when any predetermined cur} rent, which maybe measured. by the "high scale of the instrument, is flowing in'the mo tor circuits. A' double-pole single-throw the variable resistances 11 and 17 are con-. nected and the circuit which connectsthe 'free end of the movable coil 7 to one end of from the parallel circuit in which it is lo-, cated, both of the shunts 3 arid4= being includcd in parallel for the high scale reading of the instrument andonly the. shunt 3 being included in the circuit for the lower scale of The motor2 is adapted toldrive a gene'rator 14, provided "with a's liuiitifie'ld magnet' winding 15 inseries with h a'variable rcsistance;16 is connected, Assuming that the circu ings, and that the meter indi of 100 amperes supplied to t min-sedans the variable resistance'jlz'ri rke 19 x proper point of callbrat m y n wf ei; mun-m;-

Sli h ly a adjusted to bring the-ip'oin varied by regulatingY-the'fffiel the low scale meter indicatid final motor' load and 100 amperes fonfwh ch} a compensation was made in the meter coil.

As the above'examplejindicategj th tern of my inventionffm a b Care should be taken not'to omplete the circuit through theresistances 1L and 17intil the switch 13 is open,':'since' the compensating current is likely to damage the 'instruflow of current in the meter coil incident to stru'ment. which may be adiusted by openmsr and closing the switch 13."

Jtio'ns in said'values. 3. That-combination with erative effect of the neutralizing means.

I desire hat the scope of my invention shall not-be restricted to any particular type of currentvmeasuring instrument since any- -one fam1liar withthe art can easily adapt my invention 'tovarious alternating or direct current lustruments, winch may or may not be. provided with movable C01lS.'

I furthe'nde sire that only such limitations 'shall be imposed pended claims.

. I claim as my invention:

The combination with an electric circult, an electric measuring instrument therein comprising an actuating coil and means as are indicated in the ap-' for varying-the sensitiveness of the instrument, of means for neutralizing the current traversing the actuating coil and means for simultaneously mterruptmg the circuit of the actuating coil and nul'li'f ii'ng the'neutralizing' means. 'f'. 2; The comb nation with an electric cir- 1 1t-, an electric measuring instrument therethe instrument, of adjustable means "for: neutralizing; in, the movable 'coil, the eifectfof'predetermined high electric values injlthe cirquit; the instrument being thereby rendered sensitiveto relatively small varial} an electric circurt, afcurrent-indicatmg instrument there- 'IIIiCOmFllQiIg R movable coil, a pointer .op-

tralizing,'-"in the-movable coil, the effect of predetermined relatively high values of electric-current in the circuit, whereby small vari tions-from the aforesaid electric currentvalues may be indicated on the lowcurreiit scale 'of the instrument.

'-'comiected thereto and a two-scale- .dial; iind 'ineans'for varying the-current re latio 1i=-between.the electric circuit and the "movablefcoil, o f adjustable means for neun comprisinga movable coil, a pointer op eratryely connected thereto and-a two-scale" I 31nd meansfor varying the sensitlvci 4 .\.The' combination with an electric cirquit, an' electric-current rneasuring instrunt havlng an ln di ca tdr coil included there- I an'daan' "adjustable low rcsistance shunt "-'conucc tion to' said coil, of adjustable means for neutralizing the current in the indicator coil andmeans for simultaneously interrupting the circuit of the indicating coil and nullifying the effect in the neutralizing means..- Y 7 5."The combination with indicator coil, of means for neutralizing the current 1n the indicator COll at any predean electric cir-' cuit and a current meter therein having an te'rmincd value of current flowing in the circuit, so that the coil will thereafter indicate variations from said predetermined raluc, and means for simultaneously interrupting the indicator coil and annulllng the 6. The combination with an electric circuit and a current-indicating instrument therein comprising a movable coil, a pointer attached thereto, a resistance in series with said coil, and a low-resistance shunt connected in multiple-circuit with the coil and resistance, of means for neutralizing the current in the movable coil and means for simultaneously interrupting the circuit oi the movable coil and annulling the effectof the neutralizing means.

7. 'Ehe combination with an electric circuitand a current-indicating instrument therein comprising a movable coil, a pointer attached thereto, a resistance in series with said coil, and a low-resistance shunt, connected in multiple-circuit with the coil and resistance, of a variable resistance connectmi across the circuit, one end of which is connected to the junction of the coil and the resistance of the indicating instrument, and a two-pole switch that is adapted to simultaneously interrupt the variable resistance circuit and the circuit through the'movab'l'e coil. t

In testimony whereof, I have hereunto subscribed my name this 17th day of November, 1909. a

. HANS C. SPECHT. Witnesses:

R. A. MGCARTY, B. B Hnzns. 

